Improve TaskMenuView layouts for split pairs

* Instead of basing calculations on the TaskView view,
use the TaskThumbnailView as the anchor.
This helps us prevent having to re-calculate positions
that were already done to layout the thumbnails
* TODO: Gracefully handle re-positioning task menu view
on rotation

Bug: 249693334
Test: Manual, opening task menu view in
land/seascape in portrait, w/ and w/o home rotation

Change-Id: I02da96d2735657d5340e23056de69392ff8452c4